In mobile telephony systems in the GSM (Global System for Mobile communication) generation, data transmitted by radio frequency are organised in data frames divided into a plurality of time intervals with one time interval for each user and all these users can use the same frequency for communication with their mobile communication terminal. This division of data frames, called Time Division Multiple Access (TDMA) cannot give very high transmission rates (speeds).
In third generation systems, data may be transmitted using different codes that enable a plurality of mobile communication terminals to use the same radio frequency but with different codes. This technology is called Code Division Multiple Access (CDMA). Recent developments in third generation telephony networks can use the two types of radio frequency divisions for data transmission. For example UMTS-HSDPA (Universal Mobile Telecommunications System-High Speed Downlink Packet Access) type systems enable to multiplex different subscribers both in time intervals and by different codes.
For example, third generation (3G) mobile telephony networks in Europe use the UMTS (Universal Mobile Telecommunications System) standard defined by the 3GPP (Third Generation Partnership Project) standard. The WCDMA (Wide-Band Code Division Multiple Access) technology used at the moment in UMTS can give a pass band of the order of one megabyte per second. The current version of the UMTS called R99 (Release 99) is gradually being replaced by the HSDPA (High Speed Downlink Packet Access) that can achieve high pass bands for data transmission, at least in the downlink direction, in other words from emitters or Base Transceiver Stations (BTS) to mobile communication terminals present in their zone of influence (commonly called “cell”). These new transmission technologies enable operators to offer advanced new services such as videophone, Internet browsing, Multimedia Broadcast/Multicast Service (MBMS).
One problem that arises in the field of mobile telephony in general is Radio Resources Management (RRM) as a function of the topology of networks and their use by subscribers. Good exploitation (or operation) of the frequencies of a mobile telephony network actually requires optimised management of the radio resources used, both in the uplink direction and in the downlink direction. In these modern networks, transmission speeds within a network cell vary quickly and enormously as a function of the use of the different services by users. Therefore, it is important to enable efficient dynamic management of the data flow passing through Base Transceiver Stations (BTS) for the different mobile communication terminals present in their zone of influence, and to monitor the quality of services supplied. Furthermore, with the development of new technologies used in third generation systems, transmissions have become asymmetric, in other words the downlink flow (from the base transceiver station to mobile terminals) is higher than the uplink flow (from terminals to the base transceiver station). Thus for example, all that is necessary to offer multimedia broadcasting services, is to have free passband on the downlink only. The problem that then arises is to minimise the cost and radioelectric spectrum necessary to implement such asymmetric services.
Prior art describes a solution to increase the capacity of WCDMA mobile telephony networks consisting of increasing the power of the base transceiver station (BTS). However, this solution has the disadvantages that it cannot only increase the capacity in the downlink direction, while the increase in interference then limits the increase in capacity. Prior art also describes a solution that consists of using additional frequencies (a carrier). However, it is not always possible to add a carrier due to the rarity of available frequencies, and this solution is also too expensive and it cannot increase the capacity in the downlink direction only. Finally, prior art describes solutions for increasing the capacity of telephony networks due to reception diversity or emission diversity. Reception diversity consists of providing mobile communication terminals with a second antenna collecting the signal sent by base transceiver stations, in the same way as the first antenna. The mobile communication terminal then reconstructs the signal by correlating signals received by its two antennas and consequently the emission power of the base transceiver station may be reduced, which increases the network capacity correspondingly. However, this solution is not an adapted solution for broadcasting services to several mobiles because it depends on the mobile terminals in use. The power necessary for broadcasting information on the zone is fixed by the least efficient terminal. Therefore, this solution cannot be controlled by mobile telephony operators. Emission diversity consists of base transceiver stations emitting their signal on an additional transmission channel and mobile terminals then receiving two instances of the same signal so that they can more easily reconstruct said signal. The power necessary for the base transceiver station can then be reduced, which means that the network capacity can be increased. However, this solution remains expensive because it requires the addition of a transmission channel on the base transceiver stations. Therefore, it is necessary to initially select the base transceiver stations on which emission diversity has to be installed, so as to minimize the cost.
In this context, it is useful to be able to propose a solution capable of optimising the capacity of mobile telephony networks by precisely targeting the base transceiver stations on which emission diversity must be added so that downlink services can be created.